Obb 



Elastic Constants of Glass. 



Table VII.— Glass 1 b. 

 Transverse Fringes. 





After 1 Minute. 



Alter 50 Minutes. 



N. 



i(A, l+2 2 -A„2). 



A , t 2 — A 2 



i(A. K _j_2 2 — A n 2 ). A ;i + 1 2 — A n -. 



1 



•741 



■g{2 



•792 -858 



o 



•719 



•793 



•787 -799 



3 





•690 



•796 



4 



Mean Value 



•748 



•778 

 Mean Value 





■730 





•789 



• 

 Longitudinal Fringes. 



N. 



\(KW-K-y 



KA„ +6 3-v). 



1 



•160 



•158 



2 



•160 



•157 



3 



■159 



■157 



4 



•158 



•156 



5 



159 



•157 



6 



•158 



•157 





Mean Value 



Mean Value 





•159 



•157 



Examination of Results. 



The beams of glass used were all cut from good plate 

 glass free from flaws, and showed remarkably little initial 

 stress when examined under polarized light. Their surfaces, 

 however, were not optically polished, and all showed a 

 certain amount of curvature. Consequently no weight is 

 attached to the absolute values of the Elastic Constants given 

 in this paper. 



This initial irregularity in the surface of the beams may 

 also account, to some extent, for the lack of uniformity shown 

 by the cross-bending, but it is suggestive that in the cases of 



